The invention relates in general to cleaning devices and in particular to a new and useful method and apparatus for cleaning plate heat exchangers used for recovering heat from exhaust.
The invention relates particularly to a device for cleaning heat exchangers which are used for recovering heat from contaminated exhaust air, where the heat exchanger plates are arranged in a row inside the heat exchanger housing creating spaces between them and the exhaust air is passed between the heat exchanger plates.
In order to recover heat from, for example, spray-drying units, a known method is to use plate heat exchangers. In such heat exchangers, the heat exchanger plates are mounted vertically parallel to one another at intervals of 10 mm to 12 mm. The exhaust air is passed between the heat exchanger plates from above and gives up its heat to the heat carrying madium, usually water, that circulates inside the heat exchanger plates. The heated circulating water is pumped through a tube to, for example, a laminar tubular heat exchanger and there pre-heats the intake air of the spray drying unit. Since contaminated air is usually used for the heat recovery, regardless of whether it is exhaust air from the spray drying unit or from other industrial units, the plate heat exchanger must be equipped with a cleaning device. The surfaces of the heat exchanger plates are generally cleaned by applying superheated steam, water or other fluids such as compressed air. For this purpose, over the heat exchanger plates, which constitute a battery, a parallelogram-like nozzle frame is suspended, which can be moved into place over the heat exchanger plates and has spray nozzles that project the cleaning agent between the heat exchanger plates in order to spray off deposits of dirt from the exhaust air that adheres to them. The dirt is then collected in a trough under the heat exchanger plates and removed. There are several disadvantages, however, to a cleaning device of this kind. In an inoperative position, for example, the nozzle frame is positioned above the heat exchanger plates or batteries of plates and consequently is constantly exposed to the contaminated exhaust air, thus gets dirty itself and has to be cleaned in turn. Furthermore, the parallelogram-like suspension of the nozzle frame is also exposed, and its swing bearings require frequent maintenance because of the unavoidable fouling.
The invention provides a device for cleaning plate heat exchangers for recovering heat from contaminated air provides an improved cleaning method with increased security of operation and optimum cleaning efficiency and which may be carried out exceptionally well even when the heat exchanger plates are subject to extremely contaminated exhaust air. In addition, maintenance and cleaning of the device itself is reduced to a minimum.
The invention includes a cleaning device which is capable of cleaning the heat exchanger plates which have aligned through holes which receive a soot blower mounted in the wall of the housing of the plate heat exchanger. The device includes a soot blower lance which has, at least in the area of the lance head, two blower nozzles placed diametrically opposite one another. The lance is mounted so that it can be turned and moved forward. In the context of the invention, the housing wall may also be one of the two outer heat exchanger plates of a plate heat exchanger.
Soot blowers are known in the art, but are generally used to solve fouling problems encountered in the operation of boilers and industrial furnaces. The problems encountered with cleaning plate heat exchangers for recovering heat from contaminated exhaust air have in the past been neither solved nor influenced by such soot blowers. The invention is based, however, on the perception that such soot blower is also appropriate for cleaning heat exchanger plates of a plate heat exchanger that is exposed to extremely contaminated exhaust air for the sake of recovering the heat from it and to which the deposit of dirt particles that builds up on the surfaces of the heat exchanger plate therefore adheres particularly firmly. Surprisingly, the use of a soot blower in the inventive way entails only minimal losses of pressure over the height and breadth of the heat exchanger plates, even though the interval between the heat exchanger plates is usually no more than 10 mm to 12 mm. Yet perfect removal of the dirt deposit is accomplished, even near the edges of the heat exchanger plates. This may be attributable to the relatively small interval between the heat exchanger plates and the minimal drop in pressure in the cleaning agent that comes out of the blower nozzles. This cleaning agent may be the usual choice of superheated steam, water, compressed air or special cleaning fluids. It is also possible to do the cleaning with abrasives or other finely powdered solids. The cleaning may also be done according to a pre-programmed model, whereby the cleaning agents that come out of the nozzles can be of the same or of different kinds. They may be different, for instance, in order to start by moistening the contaminants and continue by softening, rinsing or blasting. Since the soot blower lance is mounted so that it can turn and be moved forward, it can be controlled in the course of the cleaning process so that the rotating blower nozzles are moved forward and back through the heat exchanger plates to be cleaned at least once, but preferably several times, so that the heat exchanger plates are subjected in the space areas repeatedly on both sides of the cleaning agent. By this means, the heat exchanger plates can be cleaned perfectly even if they are exposed to exhaust air from power plants for purposes of heat recovery.
Other features essential to the invention are explained below. The invention teaches, for instance, that the through holes are larger in diameter than the soot blower lance and that the soot blower lance is suspended on its mounting and can be moved forward through the heat exchanger plates without resting on them. In this way, the turning or rotating movement of the soot blower lance is not hampered. In a preferred embodiment of the invention, the through holes are placed in the center of the heat exchanger plates and the soot blower is mounted at the midpoint of the housing wall. Surprisingly, perfect cleaning of the heat exchanger plates is accomplished even in the far corner areas. Moreoever, in principle, it is possible to place several soot blowers side by side and/or one above the other. In addition, the soot blower lances may each have several blower nozzles distributed over their length and circumference.
In another preferred embodiment of the invention, the soot blowers are used with a plate heat exchanger where the heat exchanger plates are designed as thermal sheets. Such thermal sheets consist of two or three sheets of stainless steel welded together at precisely defined points. The sheets are expanded after welding so that a cushion-shaped intermediate space is created between the welded sheets and weld points. In this intermediate space the water to be heated, for example, or another heat carrying medium is circulated. It is important in this connection that the through holes for the soot blower lance pursuant to the invention be perfectly sealed against the escape of the heat carrying medium. An an example, the sheets may be welded together around the perimeter of the through holes so that in this area another spot weld is created that does not hamper the circulation of the heat carrying medium.
The primary advantage of the invention is that a device for cleaning plate heat exchangers for recovering the heat from contaminated exhaust air is realized that because of its improved method of operation and optimum efficiency is excellent precisely for plate heat exchangers where the heat exchanger plates are designed as thermal sheets. In any case, the soot blowers and the soot blower lance that penetrate the heat exchanger plates insure perfect cleaning of the plate surfaces and dissolve quickly even the dirt particles from the exhaust air that adhere to the corner areas. Since the soot blower lance can be virtually retracted out of the plate heat exchanger once the cleaning process is completed, it is not exposed to contaminated exhaust air itself and thus requires no cleaning of its own and is relatively maintenance-free. Overall, the cleaning device pursuant to the invention is remarkable for intensive cleaning effectiveness and trouble free operation.
Accordingly, it is an object of the invention to provide an improved method for cleaning a heat exchanger which is used for recovering heat from contaminated exhaust gases which has a plurality of hollow heat exchanger plates arranged in spaced parallel locations to which a heat exchange medium is directed and which comprises providing aligned holes in the heat exchange plates and mounting a soot blower lance on the heat exchanger so that it may be rotated and moved axially through the aligned holes and thereafter directing the cleaning medium through the lance and discharging it radially against the plates as the lance is manipulated to cover the plates with the cleaning fluid discharge as the lance is moved along and rotated relative to the holes in the heat exchanger plates.
A further object of the invention is to provide an improved device for cleaning a heat exchanger which has a plurality of spaced hollow plates through which a heat exchanger medium is directed and which comprises a plurality of holes formed in said plates in aligned relationship, a lance member mounted on the heat exchanger so that it may be rotated and moved axially to direct the lance through the holes.
A further object of the invention is to provide a device for cleaning heat exchangers which is simple in design, rugged in construction and economical to manufacture.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.